U.S. Pat. No. 4,123,480 discloses a carburetor arrangement which includes a throttle flap and a choke flap. A rotatably journalled lever is mounted on the choke shaft and this lever comes into engagement with a lever mounted on the throttle shaft so as to rotate therewith. A drag lever is mounted on the choke shaft so as to rotate therewith and is actuated by an operator-controlled element and entrains the lever, which is rotatably mounted on the choke shaft, in a rotatable direction when there is contact with a blocking element. The operator cannot bring the carburetor directly from the idle position into the warm-start position; instead, the cold-start position must first be adjusted and from there moved into the warm-start position. This manipulation is inconvenient. The manufacture of the carburetor arrangement is complex because the three levers must be arranged in defined positions relative to each other in order to ensure the function for a good starting performance.
It is an object of the invention to provide a carburetor arrangement which is simple with respect to its manipulation by an operator and in its configuration.
The carburetor arrangement of the invention is for an internal combustion engine including a two-stroke engine in a portable handheld work apparatus. The carburetor arrangement includes: a carburetor housing defining an intake channel formed therein for conducting combustion air and fuel to the engine in a predetermined flow direction; a throttle shaft rotatably mounted in the carburetor housing and a throttle flap mounted on the throttle shaft; a choke shaft rotatably mounted in the carburetor housing upstream of the throttle shaft and a choke flap mounted on the choke shaft; the throttle flap being movable from an open position, whereat the throttle flap does not significantly influence the flow in the intake channel, into a closed position whereat the throttle flap closes the intake channel; the choke flap being movable from an open position, whereat the choke flap does not significantly influence the flow in the intake channel, into a closed position whereat the choke flap closes the intake channel; the throttle flap and the choke flap being displaceable from the closed position thereof into the open position; an operator-controlled element operatively connected to the choke shaft for actuating the choke shaft; a choke lever mounted on the choke shaft so that the choke lever cannot rotate relative to the choke shaft; a throttle lever mounted on the throttle shaft so that the throttle lever cannot rotate relative to the throttle shaft; means for mutually engaging the choke lever and the throttle lever in a first angular range of the position of the choke shaft and a corresponding second angular range of the position of the throttle shaft; and, in the second angular range, an idle position, a warm-start position and a cold-start position are provided arranged one behind the other.
Only two levers are needed via which the idle position, the warm-start position and the cold-start position can be set. The levers mutually engage in both rotating directions, that is, in the closing direction as well as in the opening direction so that the sequence, in which the operating positions are set, is freely selectable. An operator can set the warm-start position as well as the cold-start position directly from the idle position and can change between these positions as desired.
The choke shaft is resiliently biased in the opening direction. For the choke flap, it can, however, be provided that it is held in the closed position and in the open position via a resiliently biased latch element which operates especially on the choke shaft. It is practical that the throttle shaft be spring biased in the closing direction. It is further provided that the resulting torque on the choke shaft acts in the closing direction of the choke flap when in the cold-start position. With this configuration, the choke flap lies seal tight in the closing direction in the intake channel section. It is practical that the throttle lever is decoupled from the choke lever in the opening direction of the throttle flap. With the choke shaft being spring biased in the opening direction, the choke flap jumps back into the idle position in this way (that is, into its open position) with the actuation of the throttle flap, for example, by means of a throttle pull acting on the throttle shaft. In this way, the operator need not reset the choke shaft into the operating position by means of the operator-controlled element; instead, this is achieved in a simple manner by pulling on the throttle.
The choke flap is mounted in the closed position with play in the closing direction in the intake channel section. The choke flap is brought into contact engagement on the intake channel section via the torque acting in the closing direction of the choke flap and being caused by the spring forces and the geometry of the levers. In this way, the choke flap can be reliably closed independently of manufacturing tolerances. In the warm-start position, the throttle lever latches into an indent in the choke lever. The levers mutually touch especially in the region of an arcuate-shaped surface. With this geometry, the torque, which is necessary in order to rotate the choke shaft, is determined by the contact points on the contact surface with the contact points being on the outside in the direction of rotation. Because of the location of the contact points, the torque can be adjusted for both rotation directions independently of each other in a specific region. In a practical manner, the throttle lever lies against a side of the choke lever in the cold-start position. In this way, the positions of the levers to each other are not precisely determined and the choke shaft can be rotated to compensate for manufacturing tolerances in the closed position until the choke flap lies against the intake channel section. The operator-controlled element engages the choke shaft via a gearing and the ratio from the operator-controlled element to the choke element is especially greater than one. The rotational angles of the choke shaft are determined by the geometry of the carburetor. With the gearing, larger rotational angles can be achieved at the operator-controlled element which facilitates the adjustability of the various positions. It can be advantageous to arrange the operator-controlled element so that it is fixed on the choke shaft so that it cannot rotate with respect thereto. In this way, an especially simple configuration of the carburetor arrangement is provided.
Advantageously, the operator-controlled element is decoupled from the choke shaft in the closed position in the closing direction and an ignition-off position is disposed at a pregiven angular distance to the normal operation position. With this configuration, no further operator-controlled elements for setting operating positions are needed. It is practical to arrange a latch element in the opening direction in the idle position which prevents an unwanted rotation of the operator-controlled element.